But most voting systems are not connected to the internet, which means they’re less prone to hacking. In fact, a 2014 report by the Presidential Commission on Election Administration, says the biggest threat on Election Day is not hackers — it’s outdated equipment.

Flip votes occur in older machines when a voter touches one name, but the machine registers another. Other times, these machines do not count the votes at all.

“My guess is that, in the context of [people discussing] ‘rigged elections,’ that stuff will become bigger in 2016,” said Lawrence Norden, deputy director of the Brennan Center’s Democracy Program. But machine failures will likely be seen “in the context of cybersecurity,” he said, instead of technological problems, “and that undermines the problem.”

Among the older machines that are vulnerable to malfunctions are Direct Record Electronic voting systems. Jurisdictions in 22 states use these machines. But it’s difficult to determine their accuracy, because some DRE systems don’t retrieve full ballot images in a readable format.

“Without a paper audit trail, the local electoral board had no way to verify whether the results were correct, but chose to accept the internal memory stick results,” said Alex Blakemore, a founding member of Virginia Verified Voting.

Fixing the problem is not cheap. A Pew Charitable Trust report estimated the newest machines cost between $2,500 and $3,000 each, and election boards need one machine for every 300 registered voters.

State and local budgets are already tight, and no federal programs specifically provide funding for upgrading voting systems.

Some cities are considering open-source systems as an inexpensive alternative. Open-source computer software means the source code is made public. It allows the public to see how the voting machines are programmed, and programmers can more easily fix glitches.

San Francisco Elections Commission decided unanimously in 2015 to develop an open-source voting system that runs on commercial off-the-shelf hardware.

That technology is still a couple years away.

Human error can also be a major problem. In 2004, machines in Carteret County, North Carolina, completely lost the votes of an estimated 4,500 people. The problem was attributed to a lack of human oversight; poll workers didn’t properly update the machines.

“Malfunctions occur, but most problems with [direct-recording electronic voting machines] can be attributed to human mistakes or procedural errors, rather than security issues,” the Congressional Research Service said in its 2005 report.

In the meantime, technology glitches can influence voter confidence and turnout and create longer lines, according to a September 2014 GAO report that studied wait times for voters in the 2012 election.